Add halfLeading to TextStyle and StrutStyle: https://github.com/flutter/engine/pull/24668

Change-Id: I5627cb163400880992db622bb887093da92d1cd5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/394969
Commit-Queue: Julia Lavrova <jlavrova@google.com>
Reviewed-by: Julia Lavrova <jlavrova@google.com>

modules/skparagraph/include/Metrics.h

@@ -69,9 +69,9 @@ public:
     // descent`. Ascent and descent are provided as positive numbers. Raw numbers
     // for specific runs of text can be obtained in run_metrics_map. These values
     // are the cumulative metrics for the entire line.
-    double fAscent = 0.0;
-    double fDescent = 0.0;
-    double fUnscaledAscent = 0.0;
+    double fAscent = SK_ScalarMax;
+    double fDescent = SK_ScalarMax;
+    double fUnscaledAscent = SK_ScalarMax;
     // Total height of the paragraph including the current line.
     //
     // The height of the current line is `round(ascent + descent)`.

modules/skparagraph/include/ParagraphStyle.h

@@ -45,10 +45,14 @@ struct StrutStyle {
     bool getHeightOverride() const { return fHeightOverride; }
     void setHeightOverride(bool v) { fHeightOverride = v; }
 
+    void setHalfLeading(bool halfLeading) { fHalfLeading = halfLeading; }
+    bool getHalfLeading() const { return fHalfLeading; }
+
     bool operator==(const StrutStyle& rhs) const {
         return this->fEnabled == rhs.fEnabled &&
                this->fHeightOverride == rhs.fHeightOverride &&
                this->fForceHeight == rhs.fForceHeight &&
+               this->fHalfLeading == rhs.fHalfLeading &&
                nearlyEqual(this->fLeading, rhs.fLeading) &&
                nearlyEqual(this->fHeight, rhs.fHeight) &&
                nearlyEqual(this->fFontSize, rhs.fFontSize) &&
@@ -66,6 +70,9 @@ private:
     bool fForceHeight;
     bool fEnabled;
     bool fHeightOverride;
+    // true: half leading.
+    // false: scale ascent/descent with fHeight.
+    bool fHalfLeading;
 };
 
 struct ParagraphStyle {

modules/skparagraph/include/TextStyle.h

@@ -221,6 +221,9 @@ public:
     void setHeightOverride(bool heightOverride) { fHeightOverride = heightOverride; }
     bool getHeightOverride() const { return fHeightOverride; }
 
+    void setHalfLeading(bool halfLeading) { fHalfLeading = halfLeading; }
+    bool getHalfLeading() const { return fHalfLeading; }
+
     void setLetterSpacing(SkScalar letterSpacing) { fLetterSpacing = letterSpacing; }
     SkScalar getLetterSpacing() const { return fLetterSpacing; }
 
@@ -262,6 +265,9 @@ private:
     SkScalar fFontSize = 14.0;
     SkScalar fHeight = 1.0;
     bool fHeightOverride = false;
+    // true: half leading.
+    // false: scale ascent/descent with fHeight.
+    bool fHalfLeading = false;
     SkString fLocale = {};
     SkScalar fLetterSpacing = 0.0;
     SkScalar fWordSpacing = 0.0;

modules/skparagraph/src/OneLineShaper.cpp

@@ -144,7 +144,8 @@ void OneLineShaper::fillGaps(size_t startingCount) {
     }
 }
 
-void OneLineShaper::finish(TextRange blockText, SkScalar height, SkScalar& advanceX) {
+void OneLineShaper::finish(const Block& block, SkScalar height, SkScalar& advanceX) {
+    auto blockText = block.fRange;
 
     // Add all unresolved blocks to resolved blocks
     while (!fUnresolvedBlocks.empty()) {
@@ -165,30 +166,30 @@ void OneLineShaper::finish(TextRange blockText, SkScalar height, SkScalar& advan
 
     // Go through all of them
     size_t lastTextEnd = blockText.start;
-    for (auto& block : fResolvedBlocks) {
+    for (auto& resolvedBlock : fResolvedBlocks) {
 
-        if (block.fText.end <= blockText.start) {
+        if (resolvedBlock.fText.end <= blockText.start) {
             continue;
         }
 
-        if (block.fRun != nullptr) {
-            fParagraph->fFontSwitches.emplace_back(block.fText.start, block.fRun->fFont);
+        if (resolvedBlock.fRun != nullptr) {
+            fParagraph->fFontSwitches.emplace_back(resolvedBlock.fText.start, resolvedBlock.fRun->fFont);
         }
 
-        auto run = block.fRun;
-        auto glyphs = block.fGlyphs;
-        auto text = block.fText;
+        auto run = resolvedBlock.fRun;
+        auto glyphs = resolvedBlock.fGlyphs;
+        auto text = resolvedBlock.fText;
         if (lastTextEnd != text.start) {
             SkDEBUGF("Text ranges mismatch: ...:%d] - [%d:%d] (%d-%d)\n", lastTextEnd, text.start, text.end,  glyphs.start, glyphs.end);
             SkASSERT(false);
         }
         lastTextEnd = text.end;
 
-        if (block.isFullyResolved()) {
+        if (resolvedBlock.isFullyResolved()) {
             // Just move the entire run
-            block.fRun->fIndex = this->fParagraph->fRuns.size();
-            this->fParagraph->fRuns.emplace_back(*block.fRun);
-            block.fRun.reset();
+            resolvedBlock.fRun->fIndex = this->fParagraph->fRuns.size();
+            this->fParagraph->fRuns.emplace_back(*resolvedBlock.fRun);
+            resolvedBlock.fRun.reset();
             continue;
         } else if (run == nullptr) {
             continue;
@@ -207,6 +208,7 @@ void OneLineShaper::finish(TextRange blockText, SkScalar height, SkScalar& advan
                     info,
                     run->fClusterStart,
                     height,
+                    block.fStyle.getHalfLeading(),
                     this->fParagraph->fRuns.count(),
                     advanceX
                 );
@@ -598,6 +600,7 @@ bool OneLineShaper::iterateThroughShapingRegions(const ShapeVisitor& shape) {
                                        runInfo,
                                        0,
                                        0.0f,
+                                       false,
                                        fParagraph->fRuns.count(),
                                        advanceX);
 
@@ -633,6 +636,7 @@ bool OneLineShaper::shape() {
 
             // Start from the beginning (hoping that it's a simple case one block - one run)
             fHeight = block.fStyle.getHeightOverride() ? block.fStyle.getHeight() : 0;
+            fUseHalfLeading = block.fStyle.getHalfLeading();
             fAdvance = SkVector::Make(advanceX, 0);
             fCurrentText = block.fRange;
             fUnresolvedBlocks.emplace_back(RunBlock(block.fRange));
@@ -696,7 +700,7 @@ bool OneLineShaper::shape() {
                 }
             });
 
-            this->finish(block.fRange, fHeight, advanceX);
+            this->finish(block, fHeight, advanceX);
         });
 
         return true;

modules/skparagraph/src/OneLineShaper.h

@@ -18,6 +18,7 @@ public:
     explicit OneLineShaper(ParagraphImpl* paragraph)
         : fParagraph(paragraph)
         , fHeight(0.0f)
+        , fUseHalfLeading(false)
         , fAdvance(SkPoint::Make(0.0f, 0.0f))
         , fUnresolvedGlyphs(0)
         , fUniqueRunId(paragraph->fRuns.size()){ }
@@ -69,7 +70,7 @@ private:
 #ifdef SK_DEBUG
     void printState();
 #endif
-    void finish(TextRange text, SkScalar height, SkScalar& advanceX);
+    void finish(const Block& block, SkScalar height, SkScalar& advanceX);
 
     void beginLine() override {}
     void runInfo(const RunInfo&) override {}
@@ -81,6 +82,7 @@ private:
                                            info,
                                            fCurrentText.start,
                                            fHeight,
+                                           fUseHalfLeading,
                                            ++fUniqueRunId,
                                            fAdvance.fX);
         return fCurrentRun->newRunBuffer();
@@ -101,6 +103,7 @@ private:
     ParagraphImpl* fParagraph;
     TextRange fCurrentText;
     SkScalar fHeight;
+    bool fUseHalfLeading;
     SkVector fAdvance;
     size_t fUnresolvedGlyphs;
     size_t fUniqueRunId;

modules/skparagraph/src/ParagraphImpl.cpp

@@ -914,11 +914,20 @@ void ParagraphImpl::computeEmptyMetrics() {
             fEmptyMetrics.leading());
     } else if (!paragraphStyle().getStrutStyle().getForceStrutHeight() &&
         textStyle.getHeightOverride()) {
-        auto multiplier = textStyle.getHeight() * textStyle.getFontSize() / fEmptyMetrics.height();
-        fEmptyMetrics.update(
-            fEmptyMetrics.ascent() * multiplier,
-            fEmptyMetrics.descent() * multiplier,
-            fEmptyMetrics.leading() * multiplier);
+        const auto intrinsicHeight = fEmptyMetrics.height();
+        const auto strutHeight = textStyle.getHeight() * textStyle.getFontSize();
+        if (paragraphStyle().getStrutStyle().getHalfLeading()) {
+            fEmptyMetrics.update(
+                fEmptyMetrics.ascent(),
+                fEmptyMetrics.descent(),
+                fEmptyMetrics.leading() + strutHeight - intrinsicHeight);
+        } else {
+            const auto multiplier = strutHeight / intrinsicHeight;
+            fEmptyMetrics.update(
+                fEmptyMetrics.ascent() * multiplier,
+                fEmptyMetrics.descent() * multiplier,
+                fEmptyMetrics.leading() * multiplier);
+        }
     }
 
     if (fParagraphStyle.getStrutStyle().getStrutEnabled()) {

modules/skparagraph/src/ParagraphStyle.cpp

@@ -16,6 +16,7 @@ StrutStyle::StrutStyle() {
     fLeading = -1;
     fForceHeight = false;
     fHeightOverride = false;
+    fHalfLeading = false;
     fEnabled = false;
 }
 

modules/skparagraph/src/Run.cpp

@@ -18,6 +18,7 @@ Run::Run(ParagraphImpl* owner,
          const SkShaper::RunHandler::RunInfo& info,
          size_t firstChar,
          SkScalar heightMultiplier,
+         bool useHalfLeading,
          size_t index,
          SkScalar offsetX)
     : fOwner(owner)
@@ -26,6 +27,7 @@ Run::Run(ParagraphImpl* owner,
     , fFont(info.fFont)
     , fClusterStart(firstChar)
     , fHeightMultiplier(heightMultiplier)
+    , fUseHalfLeading(useHalfLeading)
 {
     fBidiLevel = info.fBidiLevel;
     fAdvance = info.fAdvance;
@@ -53,9 +55,17 @@ void Run::calculateMetrics() {
     fCorrectAscent = fFontMetrics.fAscent - fFontMetrics.fLeading * 0.5;
     fCorrectDescent = fFontMetrics.fDescent + fFontMetrics.fLeading * 0.5;
     fCorrectLeading = 0;
-    if (!SkScalarNearlyZero(fHeightMultiplier)) {
-        auto multiplier = fHeightMultiplier * fFont.getSize() /
-                             (fFontMetrics.fDescent - fFontMetrics.fAscent + fFontMetrics.fLeading);
+    if (SkScalarNearlyZero(fHeightMultiplier)) {
+        return;
+    }
+    const auto runHeight = fHeightMultiplier * fFont.getSize();
+    const auto fontIntrinsicHeight = fCorrectDescent - fCorrectAscent;
+    if (fUseHalfLeading) {
+        const auto extraLeading = (runHeight - fontIntrinsicHeight) / 2;
+        fCorrectAscent -= extraLeading;
+        fCorrectDescent += extraLeading;
+    } else {
+        const auto multiplier = runHeight / fontIntrinsicHeight;
         fCorrectAscent *= multiplier;
         fCorrectDescent *= multiplier;
     }

modules/skparagraph/src/Run.h

@@ -58,6 +58,7 @@ public:
         const SkShaper::RunHandler::RunInfo& info,
         size_t firstChar,
         SkScalar heightMultiplier,
+        bool useHalfLeading,
         size_t index,
         SkScalar shiftX);
     Run(const Run&) = default;
@@ -95,6 +96,7 @@ public:
     TextDirection getTextDirection() const { return leftToRight() ? TextDirection::kLtr : TextDirection::kRtl; }
     size_t index() const { return fIndex; }
     SkScalar heightMultiplier() const { return fHeightMultiplier; }
+    bool useHalfLeading() const { return fUseHalfLeading; }
     PlaceholderStyle* placeholderStyle() const;
     bool isPlaceholder() const { return fPlaceholderIndex != std::numeric_limits<size_t>::max(); }
     size_t clusterIndex(size_t pos) const { return fClusterIndexes[pos]; }
@@ -190,6 +192,7 @@ private:
 
     SkFontMetrics fFontMetrics;
     const SkScalar fHeightMultiplier;
+    const bool fUseHalfLeading;
     SkScalar fCorrectAscent;
     SkScalar fCorrectDescent;
     SkScalar fCorrectLeading;
@@ -382,7 +385,6 @@ public:
     }
 
     void add(Run* run) {
-
         if (fForceStrut) {
             return;
         }
@@ -406,11 +408,11 @@ public:
     }
 
     void clean() {
-        fAscent = 0;
-        fDescent = 0;
+        fAscent = SK_ScalarMax;
+        fDescent = SK_ScalarMin;
         fLeading = 0;
-        fRawAscent = 0;
-        fRawDescent = 0;
+        fRawAscent = SK_ScalarMax;
+        fRawDescent = SK_ScalarMin;
         fRawLeading = 0;
     }
 

modules/skparagraph/src/TextLine.cpp

@@ -531,8 +531,8 @@ std::unique_ptr<Run> TextLine::shapeEllipsis(const SkString& ellipsis, const Run
 
     class ShapeHandler final : public SkShaper::RunHandler {
     public:
-        ShapeHandler(SkScalar lineHeight, const SkString& ellipsis)
-            : fRun(nullptr), fLineHeight(lineHeight), fEllipsis(ellipsis) {}
+        ShapeHandler(SkScalar lineHeight, bool useHalfLeading, const SkString& ellipsis)
+            : fRun(nullptr), fLineHeight(lineHeight), fUseHalfLeading(useHalfLeading), fEllipsis(ellipsis) {}
         Run* run() & { return fRun.get(); }
         std::unique_ptr<Run> run() && { return std::move(fRun); }
 
@@ -545,7 +545,7 @@ std::unique_ptr<Run> TextLine::shapeEllipsis(const SkString& ellipsis, const Run
 
         Buffer runBuffer(const RunInfo& info) override {
             SkASSERT(!fRun);
-            fRun = std::make_unique<Run>(nullptr, info, 0, fLineHeight, 0, 0);
+            fRun = std::make_unique<Run>(nullptr, info, 0, fLineHeight, fUseHalfLeading, 0, 0);
             return fRun->newRunBuffer();
         }
 
@@ -560,10 +560,11 @@ std::unique_ptr<Run> TextLine::shapeEllipsis(const SkString& ellipsis, const Run
 
         std::unique_ptr<Run> fRun;
         SkScalar fLineHeight;
+        bool fUseHalfLeading;
         SkString fEllipsis;
     };
 
-    ShapeHandler handler(run.heightMultiplier(), ellipsis);
+    ShapeHandler handler(run.heightMultiplier(), run.useHalfLeading(), ellipsis);
     std::unique_ptr<SkShaper> shaper = SkShaper::MakeShapeDontWrapOrReorder();
     SkASSERT_RELEASE(shaper != nullptr);
     shaper->shape(ellipsis.c_str(), ellipsis.size(), run.font(), true,
@@ -1010,13 +1011,12 @@ void TextLine::getRectsForRange(TextRange textRange0,
                 }
                 break;
                 case RectHeightStyle::kTight: {
-                    if (run->fHeightMultiplier > 0) {
-                        // This is a special case when we do not need to take in account this height multiplier
-                        auto correctedHeight = clip.height() / run->fHeightMultiplier;
-                        auto verticalShift =  this->sizes().runTop(context.run, LineMetricStyle::Typographic);
-                        clip.fTop += verticalShift;
-                        clip.fBottom = clip.fTop + correctedHeight;
+                    if (run->fHeightMultiplier <= 0) {
+                        break;
                     }
+                    const auto effectiveBaseline = this->baseline() + this->sizes().delta();
+                    clip.fTop = effectiveBaseline + run->ascent();
+                    clip.fBottom = effectiveBaseline + run->descent();
                 }
                 break;
                 default:

modules/skparagraph/src/TextStyle.cpp

@@ -20,6 +20,7 @@ TextStyle::TextStyle(const TextStyle& other, bool placeholder) {
     fHeightOverride = other.fHeightOverride;
     fIsPlaceholder = placeholder;
     fFontFeatures = other.fFontFeatures;
+    fHalfLeading = other.fHalfLeading;
 }
 
 bool TextStyle::equals(const TextStyle& other) const {
@@ -49,6 +50,9 @@ bool TextStyle::equals(const TextStyle& other) const {
     if (fHeight != other.fHeight) {
         return false;
     }
+    if (fHalfLeading != other.fHalfLeading) {
+        return false;
+    }
     if (fFontSize != other.fFontSize) {
         return false;
     }
@@ -134,7 +138,8 @@ bool TextStyle::matchOneAttribute(StyleType styleType, const TextStyle& other) c
                    fLocale == other.fLocale &&
                    fFontFamilies == other.fFontFamilies &&
                    fFontSize == other.fFontSize &&
-                   fHeight == other.fHeight;
+                   fHeight == other.fHeight &&
+                   fHalfLeading == other.fHalfLeading;
         default:
             SkASSERT(false);
             return false;

modules/skparagraph/tests/SkParagraphTest.cpp

@@ -1267,6 +1267,293 @@ DEF_TEST(SkParagraph_HeightOverrideParagraph, reporter) {
     REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[1].rect.bottom(), 165.495f, EPSILON5));
 }
 
+DEF_TEST(SkParagraph_BasicHalfLeading, reporter) {
+    sk_sp<ResourceFontCollection> fontCollection = sk_make_sp<ResourceFontCollection>();
+
+    if (!fontCollection->fontsFound()) {
+      return;
+    }
+
+    const char* text = "01234満毎冠行来昼本可\nabcd\n満毎冠行来昼本可";
+    const size_t len = strlen(text);
+
+    TestCanvas canvas("SkParagraph_BasicHalfLeading.png");
+
+    ParagraphStyle paragraph_style;
+    TextStyle text_style;
+    text_style.setFontFamilies({SkString("Roboto")});
+    text_style.setFontSize(20.0f);
+    text_style.setColor(SK_ColorBLACK);
+    text_style.setLetterSpacing(0.0f);
+    text_style.setWordSpacing(0.0f);
+    text_style.setHeightOverride(true);
+    text_style.setHeight(3.6345f);
+    text_style.setHalfLeading(true);
+
+    ParagraphBuilderImpl builder(paragraph_style, fontCollection);
+
+    builder.pushStyle(text_style);
+    builder.addText(text);
+
+    auto paragraph = builder.Build();
+    paragraph->layout(550);
+
+    auto impl = static_cast<ParagraphImpl*>(paragraph.get());
+    REPORTER_ASSERT(reporter, impl->styles().size() == 1);  // paragraph style does not count
+    REPORTER_ASSERT(reporter, impl->styles()[0].fStyle.equals(text_style));
+
+    paragraph->paint(canvas.get(), 0, 0);
+
+    const RectWidthStyle rect_width_style = RectWidthStyle::kTight;
+    std::vector<TextBox> boxes = paragraph->getRectsForRange(0, len, RectHeightStyle::kTight, rect_width_style);
+    std::vector<TextBox> lineBoxes = paragraph->getRectsForRange(0, len, RectHeightStyle::kMax, rect_width_style);
+
+    canvas.drawRects(SK_ColorBLUE, boxes);
+    REPORTER_ASSERT(reporter, boxes.size() == 3ull);
+    REPORTER_ASSERT(reporter, lineBoxes.size() == boxes.size());
+
+    const auto line_spacing1 = boxes[1].rect.top() - boxes[0].rect.bottom();
+    const auto line_spacing2 = boxes[2].rect.top() - boxes[1].rect.bottom();
+
+    // Uniform line spacing.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(line_spacing1, line_spacing2));
+
+    // line spacing is distributed evenly over and under the text.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[0].rect.bottom() - boxes[0].rect.bottom(), boxes[0].rect.top() - lineBoxes[0].rect.top()));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[1].rect.bottom() - boxes[1].rect.bottom(), boxes[1].rect.top() - lineBoxes[1].rect.top()));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[2].rect.bottom() - boxes[2].rect.bottom(), boxes[2].rect.top() - lineBoxes[2].rect.top()));
+
+    // Half leading does not move the text horizontally.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[1].rect.left(), 0, EPSILON100));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[1].rect.right(), 43.843f, EPSILON100));
+}
+
+DEF_TEST(SkParagraph_NearZeroHeightMixedDistribution, reporter) {
+    sk_sp<ResourceFontCollection> fontCollection = sk_make_sp<ResourceFontCollection>();
+
+    if (!fontCollection->fontsFound()) {
+      return;
+    }
+
+    const char* text = "Cookies need love";
+    const size_t len = strlen(text);
+
+    TestCanvas canvas("SkParagraph_ZeroHeightHalfLeading.png");
+
+    ParagraphStyle paragraph_style;
+    paragraph_style.setTextHeightBehavior(TextHeightBehavior::kAll);
+    TextStyle text_style;
+    text_style.setFontFamilies({SkString("Roboto")});
+    text_style.setFontSize(20.0f);
+    text_style.setColor(SK_ColorBLACK);
+    text_style.setLetterSpacing(0.0f);
+    text_style.setWordSpacing(0.0f);
+    text_style.setHeightOverride(true);
+    text_style.setHeight(0.001f);
+
+    ParagraphBuilderImpl builder(paragraph_style, fontCollection);
+
+    // First run, half leading.
+    text_style.setHalfLeading(true);
+    builder.pushStyle(text_style);
+    builder.addText(text);
+
+    // Second run, no half leading.
+    text_style.setHalfLeading(false);
+    builder.pushStyle(text_style);
+    builder.addText(text);
+
+    auto paragraph = builder.Build();
+    paragraph->layout(550);
+    paragraph->paint(canvas.get(), 0, 0);
+
+    auto impl = static_cast<ParagraphImpl*>(paragraph.get());
+    REPORTER_ASSERT(reporter, impl->runs().size() == 2);
+    REPORTER_ASSERT(reporter, impl->styles().size() == 2);  // paragraph style does not count
+    REPORTER_ASSERT(reporter, impl->lines().size() == 1ull);
+
+    const RectWidthStyle rect_width_style = RectWidthStyle::kTight;
+
+    std::vector<TextBox> boxes = paragraph->getRectsForRange(0, len, RectHeightStyle::kTight, rect_width_style);
+    std::vector<TextBox> lineBoxes = paragraph->getRectsForRange(0, len, RectHeightStyle::kMax, rect_width_style);
+
+    canvas.drawRects(SK_ColorBLUE, boxes);
+    REPORTER_ASSERT(reporter, boxes.size() == 1ull);
+    REPORTER_ASSERT(reporter, lineBoxes.size() == boxes.size());
+
+    // From font metrics.
+    const auto metricsAscent = -18.5546875f;
+    const auto metricsDescent = 4.8828125f;
+
+    // As the height multiplier converges to 0 (but not 0 since 0 is used as a
+    // magic value to indicate there's no height multiplier), the `Run`s top
+    // edge and bottom edge will converge to a horizontal line:
+    // - When half leading is used the vertical line is roughly the center of
+    //   of the glyphs in the run ((fontMetrics.descent - fontMetrics.ascent) / 2)
+    // - When half leading is disabled the line is the alphabetic baseline.
+
+    // Expected values in baseline coordinate space:
+    const auto run1_ascent = (metricsAscent + metricsDescent) / 2;
+    const auto run1_descent = (metricsAscent + metricsDescent) / 2;
+    const auto run2_ascent = 0.0f;
+    const auto run2_descent = 0.0f;
+    const auto line_top = std::min(run1_ascent, run2_ascent);
+    const auto line_bottom = std::max(run1_descent, run2_descent);
+
+    // Expected glyph height in linebox coordinate space:
+    const auto glyphs_top = metricsAscent - line_top;
+    const auto glyphs_bottom = metricsDescent - line_top;
+
+    // kTight reports the glyphs' bounding box in the linebox's coordinate
+    // space.
+    const auto actual_glyphs_top = boxes[0].rect.top() - lineBoxes[0].rect.top();
+    const auto actual_glyphs_bottom = boxes[0].rect.bottom() - lineBoxes[0].rect.top();
+
+    // Use a relatively large epsilon since the heightMultiplier is not actually
+    // 0.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(glyphs_top, actual_glyphs_top, EPSILON20));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(glyphs_bottom, actual_glyphs_bottom, EPSILON20));
+
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[0].rect.height(), line_bottom - line_top, EPSILON2));
+    REPORTER_ASSERT(reporter, lineBoxes[0].rect.height() > 1);
+
+    // Half leading does not move the text horizontally.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[0].rect.left(), 0, EPSILON100));
+}
+
+DEF_TEST(SkParagraph_StrutHalfLeading, reporter) {
+    sk_sp<ResourceFontCollection> fontCollection = sk_make_sp<ResourceFontCollection>();
+
+    if (!fontCollection->fontsFound()) {
+      return;
+    }
+
+    const char* text = "01234満毎冠行来昼本可\nabcd\n満毎冠行来昼本可";
+    const size_t len = strlen(text);
+
+    TestCanvas canvas("SkParagraph_StrutHalfLeading.png");
+
+    ParagraphStyle paragraph_style;
+    // Tiny font and height multiplier to ensure the height is entirely decided
+    // by the strut.
+    TextStyle text_style;
+    text_style.setFontFamilies({SkString("Roboto")});
+    text_style.setFontSize(1.0f);
+    text_style.setColor(SK_ColorBLACK);
+    text_style.setLetterSpacing(0.0f);
+    text_style.setWordSpacing(0.0f);
+    text_style.setHeight(0.1f);
+
+    StrutStyle strut_style;
+    strut_style.setFontFamilies({SkString("Roboto")});
+    strut_style.setFontSize(20.0f);
+    strut_style.setHeight(3.6345f);
+    strut_style.setHalfLeading(true);
+    strut_style.setStrutEnabled(true);
+    strut_style.setForceStrutHeight(true);
+
+    ParagraphBuilderImpl builder(paragraph_style, fontCollection);
+
+    builder.pushStyle(text_style);
+    builder.addText(text);
+
+    auto paragraph = builder.Build();
+    paragraph->layout(550);
+
+    auto impl = static_cast<ParagraphImpl*>(paragraph.get());
+    REPORTER_ASSERT(reporter, impl->styles().size() == 1);  // paragraph style does not count
+
+    paragraph->paint(canvas.get(), 0, 0);
+
+    const RectWidthStyle rect_width_style = RectWidthStyle::kTight;
+    std::vector<TextBox> boxes = paragraph->getRectsForRange(0, len, RectHeightStyle::kTight, rect_width_style);
+    std::vector<TextBox> lineBoxes = paragraph->getRectsForRange(0, len, RectHeightStyle::kMax, rect_width_style);
+
+    canvas.drawRects(SK_ColorBLUE, boxes);
+    REPORTER_ASSERT(reporter, boxes.size() == 3ull);
+    REPORTER_ASSERT(reporter, lineBoxes.size() == boxes.size());
+
+    const auto line_spacing1 = boxes[1].rect.top() - boxes[0].rect.bottom();
+    const auto line_spacing2 = boxes[2].rect.top() - boxes[1].rect.bottom();
+
+    // Uniform line spacing.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(line_spacing1, line_spacing2));
+
+    // line spacing is distributed evenly over and under the text.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[0].rect.bottom() - boxes[0].rect.bottom(), boxes[0].rect.top() - lineBoxes[0].rect.top()));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[1].rect.bottom() - boxes[1].rect.bottom(), boxes[1].rect.top() - lineBoxes[1].rect.top()));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[2].rect.bottom() - boxes[2].rect.bottom(), boxes[2].rect.top() - lineBoxes[2].rect.top()));
+
+    // Half leading does not move the text horizontally.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[1].rect.left(), 0, EPSILON100));
+}
+
+DEF_TEST(SkParagraph_TrimLeadingDistribution, reporter) {
+    sk_sp<ResourceFontCollection> fontCollection = sk_make_sp<ResourceFontCollection>();
+
+    if (!fontCollection->fontsFound()) {
+      return;
+    }
+
+    const char* text = "01234満毎冠行来昼本可\nabcd\n満毎冠行来昼本可";
+    const size_t len = strlen(text);
+
+    TestCanvas canvas("SkParagraph_TrimHalfLeading.png");
+
+    ParagraphStyle paragraph_style;
+    paragraph_style.setTextHeightBehavior(TextHeightBehavior::kDisableAll);
+    TextStyle text_style;
+    text_style.setFontFamilies({SkString("Roboto")});
+    text_style.setFontSize(20.0f);
+    text_style.setColor(SK_ColorBLACK);
+    text_style.setLetterSpacing(0.0f);
+    text_style.setWordSpacing(0.0f);
+    text_style.setHeightOverride(true);
+    text_style.setHeight(3.6345f);
+    text_style.setHalfLeading(true);
+
+    ParagraphBuilderImpl builder(paragraph_style, fontCollection);
+
+    builder.pushStyle(text_style);
+    builder.addText(text);
+
+    auto paragraph = builder.Build();
+    paragraph->layout(550);
+    paragraph->paint(canvas.get(), 0, 0);
+
+    const RectWidthStyle rect_width_style = RectWidthStyle::kTight;
+
+    std::vector<TextBox> boxes = paragraph->getRectsForRange(0, len, RectHeightStyle::kTight, rect_width_style);
+    std::vector<TextBox> lineBoxes = paragraph->getRectsForRange(0, len, RectHeightStyle::kMax, rect_width_style);
+
+    canvas.drawRects(SK_ColorBLUE, boxes);
+    REPORTER_ASSERT(reporter, boxes.size() == 3ull);
+    REPORTER_ASSERT(reporter, lineBoxes.size() == boxes.size());
+
+    const auto line_spacing1 = boxes[1].rect.top() - boxes[0].rect.bottom();
+    const auto line_spacing2 = boxes[2].rect.top() - boxes[1].rect.bottom();
+
+    // Uniform line spacing. The delta is introduced by the height rounding.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(line_spacing1, line_spacing2, 1));
+
+    // Trim the first line's top leading.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[0].rect.top(), boxes[0].rect.top()));
+    // Trim the last line's bottom leading.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[2].rect.bottom(), boxes[2].rect.bottom()));
+
+    const auto halfLeading =  lineBoxes[0].rect.bottom() - boxes[0].rect.bottom();
+    // Large epsilon because of rounding.
+    const auto epsilon = EPSILON10;
+    // line spacing is distributed evenly over and under the text.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[1].rect.top() - lineBoxes[1].rect.top(), halfLeading, epsilon));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(lineBoxes[1].rect.bottom() - boxes[1].rect.bottom(),  halfLeading));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[2].rect.top() - lineBoxes[2].rect.top(), halfLeading, epsilon));
+
+    // Half leading does not move the text horizontally.
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[1].rect.left(), 0, EPSILON100));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(boxes[1].rect.right(), 43.843f, EPSILON100));
+}
+
 DEF_TEST(SkParagraph_LeftAlignParagraph, reporter) {
     sk_sp<ResourceFontCollection> fontCollection = sk_make_sp<ResourceFontCollection>();
     if (!fontCollection->fontsFound()) return;